It is well known that micronised waxes will impart desirable features to paint or lacquer film or coatings (e.g., flexibility, feel and gloss). Inorganic oxide particulates have also been used to import matting to the coating. When an inorganic oxide particulate is coated/impregnated with wax a process usually performed by jointly grinding the oxide particulate and wax in a fluid energy mill (microniser), further product benefits are immediately available. The wax can improve compatibility of the oxide particulate with the paint or lacquer preventing interaction with other components in the formulation, but another function is to prevent the formation of hard sediment during storage, which is not redispersible. Whilst the mechanism by which this protection is afforded is still not fully understood, its benefit to the paint or lacquer manufacturer is widely recognized because, if hard sediments that cannot be redispersed are formed, none of the benefits described above can be realized.
Two types of wax-coated oxide particulates are generally disclosed in the literature. GB Patent No. 798,621 discloses a silica-matting agent produced by co-milling an intermediate density silica gel with a microcrystalline wax in a fluid energy mill. GB Patent No. 1,236,775 teaches a silica matting agent can be prepared by treating precipitated silica with an aqueous emulsion or dispersion of a wax, including thermoplastic materials. The properties of the silica matting agents prepared by the so-called “dry” co-micronising route have been further improved by adding fatty acids (GB Patent No. 1,461,511) or synthetic polyethylene waxes of varying molecular weight (U.S. Pat. No. 4,097,302) to the microcrystalline wax before feeding to the fluid energy mill. The former improves the dispersibility of the wax coated products, whereas the latter shows products having enhanced settlement characteristics compared with commercially available materials. The “dry” processing routes described above use temperatures in excess of the melting points of the waxes or wax blends whereas GB Patent No. 1,538,474 discloses a process which can produce satisfactory wax coated silicas at micronising temperatures of below 50° C., where functional waxes such as montan acid ester are employed.
U.S. Pat. No. 5,326,395 describes a matting agent that utilizes a ternary blend of waxes, including a hard microcrystalline wax, a plasticizing microcrystalline wax, and a synthetic polyethylene wax, that is coated on a silica particulate. U.S. Patent Application No. 2004/0047792 A1 relates to a wax coated precipitated silica matting agent wherein the wax may include polyethylene waxes, Fischer-Tropsch waxes, or silicone waxes.
U.S. Pat. No. 6,761,764 B2 describes the use of wax particles, without an inorganic oxide component, for use as matting agents in various coatings. The waxes used include a mixture of olefin waxes and various other waxes.
There remains a need in the coating industry for an inorganic oxide matting agent that provides acceptable matting properties while also providing improved abrasion resistance and chemical stability.